Adding upstream version 14.2.21.upstream/14.2.21upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 72 insertions, 0 deletions

diff --git a/src/boost/libs/yap/example/transform_terminals.cpp b/src/boost/libs/yap/example/transform_terminals.cpp
new file mode 100644
index 00000000..2bab93d6
--- /dev/null
+++ b/src/boost/libs/yap/example/transform_terminals.cpp
@@ -0,0 +1,72 @@
+// Copyright (C) 2016-2018 T. Zachary Laine
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//[ transform_terminals
+#include <boost/yap/yap.hpp>
+
+
+struct iota_terminal_transform
+{
+    // Base case. Note that we're not treating placeholders specially for this
+    // example (they're easy to special-case if necessary).
+    template<typename T>
+    auto operator()(boost::yap::expr_tag<boost::yap::expr_kind::terminal>, T && t)
+    {
+        // Like the std::iota() algorithm, we create replacement int terminals
+        // with the values index_, index_ + 1, index_ + 2, etc.
+        return boost::yap::make_terminal(index_++);
+    }
+
+    // Recursive case: Match any call expression.
+    template<typename CallableExpr, typename... Arg>
+    auto operator()(boost::yap::expr_tag<boost::yap::expr_kind::call>,
+                    CallableExpr callable, Arg &&... arg)
+    {
+        // Even though the callable in a call expression is technically a
+        // terminal, it doesn't make a lot of sense to replace it with an int,
+        // so we'll only transform the argument subexpressions.
+        return boost::yap::make_expression<boost::yap::expr_kind::call>(
+            boost::yap::as_expr(callable),
+            boost::yap::transform(boost::yap::as_expr(arg), *this)...);
+    }
+
+    int index_;
+};
+
+int sum(int a, int b) { return a + b; }
+
+int main()
+{
+    {
+        // This simple sum(8, 8) expression requires both overloads of
+        // iota_terminal_transform.
+        auto expr = boost::yap::make_terminal(sum)(8, 8);
+        assert(evaluate(expr) == 16);
+
+        auto iota_expr = boost::yap::transform(expr, iota_terminal_transform{1});
+        assert(evaluate(iota_expr) == 3);
+    }
+
+    {
+        // This expression requires only the terminal case of
+        // iota_terminal_transform.
+        auto expr = -(boost::yap::make_terminal(8) + 8);
+        assert(evaluate(expr) == -16);
+
+        auto iota_expr = boost::yap::transform(expr, iota_terminal_transform{0});
+        assert(evaluate(iota_expr) == -1);
+    }
+
+    {
+        // Like the first expression above, this expression requires both
+        // overloads of iota_terminal_transform.
+        auto expr = boost::yap::make_terminal(sum)(-(boost::yap::make_terminal(8) + 8), 0);
+        assert(evaluate(expr) == -16);
+
+        auto iota_expr = boost::yap::transform(expr, iota_terminal_transform{0});
+        assert(evaluate(iota_expr) == -3);
+    }
+}
+//]